kunit: drop unused intermediate macros for ptr inequality checks

We have the intermediate macros for KUNIT_EXPECT_PTR_GT() and friends,
but these macros don't exist.

I can see niche usecases for these macros existing, but since we've been
fine without them for so long, let's drop this dead code.

Users can instead cast the pointers and use the other GT/LT macros.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>